As a next-generation system of the W-CDMA (Wideband Code Division Multiple Access) and the HSDPA (High Speed Downlink Packet Access), an LTE system has been studied by 3GPP (3rd Generation Partnership Project) which is a standards body of the W-CDMA. In the LTE system as a radio access system, an OFDM (Orthogonal Frequency Division Multiplexing) scheme and an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme have been studied to be applied to the downlink communications system and the uplink communication system, respectively (see, for example, Non Patent Document 1).
In the OFDM scheme, a frequency band is divided into plural sub-carriers having narrower frequency bands, and data are transmitted on each sub frequency band and the sub-carriers are closely arranged so as not to interfere with each other, so that fast data transmission can be achieved and an efficiency use of the frequency band can be improved.
In the SC-FDMA scheme, a frequency band is divided in a manner so that different frequencies can be separately used among plural terminals (user equipment terminals) and as a result, interferences between terminals can be reduced. Further, in the SC-FDMA scheme, a range of transmission power fluctuation can be made smaller; therefore lower energy consumption of terminals can be achieved and a wider coverage area can be obtained.
In the LTE system, communications are performed by sharing one or more physical channels among plural mobile stations (user equipment (UE) terminals). The channel shared among plural mobile terminals is generally called a shared channel. In the LTE system, a Physical Uplink Shared Channel (PUSCH) and a Physical Downlink Shared Channel (PDSCH) are the shared channels in uplink and downlink, respectively. Further, the transport channels (TrCH) to be mapped over the PUSCH and PDSCH are an Uplink-Shared Channel (UL-SCH) and a Downlink-Shared Channel (DL-SCH), respectively.
Further, in a communication system using the shared channels as described above, signaling is required for allocating the shared channels to the corresponding mobile stations (UE terminals) in each sub-frame. In the LTE system, the channel used for the signaling is called a Physical Downlink Control Channel (PDCCH) or Downlink L1/L2 Control Channel (DL L1/L2 Control channel). The information items of the Physical Downlink Control Channel (PDCCH) includes, for example, a DL L1/L2 Control Channel Format Indicator, DL (Downlink) Scheduling Information, Acknowledgement information (UL ACK/NACK), Uplink Scheduling Grant, an Overload Indicator, and a Transmission Power Control Command Bit (TPC bit) (see Non Patent Document 2). The DL L1/L2 Control Format Indicator may also be called a Physical Control Format Indicator Channel (PCFICH), and the UL ACK/NACK may also be called a Physical Hybrid ARQ Indicator Channel (PHICH). However, the PCFICH and the PHICH are not necessarily included in the PDCCH and may be defined as separate physical channels having a parallel relationship with the Physical Downlink Control Channel (PDCCH).
Further, the DL Scheduling Information includes, for example, allocation information of downlink resource blocks, an ID of user equipment (UE) (hereinafter may be referred to as a user equipment (UE) terminal), the number of streams, information of a Precoding Vector, data size, a modulation scheme, and information of HARQ (Hybrid Automatic Repeat reQuest). The DL Scheduling Information may also be called DL Assignment Information or DL Scheduling Grant. Further, the UL Scheduling Grant includes, for example, allocation information of uplink resource blocks, the ID of user equipment (UE), the data size, the modulation scheme, power information of the uplink transmission, and information of a Demodulation Reference Signal.
The Physical Downlink Control Channel (PDCCH) is transmitted by using first L symbols (L=1, 2, 3) in one sub-frame (see Non Patent Document 3). Further, in the first L symbol(s) of the PDCCH, the information items of the PDCCH are being multiplexed, the information items including, more specifically, the DL L1/L2 Control Channel Format Indicator, the Downlink Scheduling Information, the Acknowledgement information (UL ACK/NACK), the Uplink Scheduling Grant, the Overload Indicator, and the Transmission Power Control Command Bit (TPC bit). In this case, in order to efficiently multiplex the information items of the PDCCH, transmission power control is applied to each of the information items of the PDCCH.    Non Patent Document 1: 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006    Non Patent Document 2: R1-070103, Downlink L1/L2 Control Signaling Channel Structure: Coding    Non Patent Document 3: 3GPP TS 36.211 (v 0.3.1), “Physical Channels and Modulation,” February 2007    Non Patent Document 4: R1-070105, ACK/NACK Signal Structure in E-UTRA Downlink, January 2007